Re: [MMUSIC] Comments on mmusic-data-channel-sdpneg-05
Gunnar Hellström <gunnar.hellstrom@omnitor.se> Fri, 09 October 2015 18:43 UTC
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From: Gunnar Hellström <gunnar.hellstrom@omnitor.se>
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Date: Fri, 09 Oct 2015 20:42:39 +0200
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Subject: Re: [MMUSIC] Comments on mmusic-data-channel-sdpneg-05
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Juergen, Accepted as commented below, Den 2015-10-09 kl. 17:22, skrev Juergen Stoetzer-Bradler: > Hello Gunnar, > > Thanks much for your comments. > I've inserted my replies below. > > Thank you, > Juergen > > On 09.10.2015 09:44, Gunnar Hellström wrote: >> mmusic-data-channel looks good. >> >> I have some minor comments: >> There are left-overs from when it was MSRP-specific that is confusing >> for a reader now. >> Suggestions: >> >> 1. In 5.1.2.1, change this: >> ------------------------------------------------------------------------ >> >> which specifies that this instance of MSRP >> --------------------------------------------------- >> >> to >> ----------------------------------------------------------------------- >> >> which specifies that this instance of the subprotocol >> -------------------------------------------------- >> Because before that point there has not been any discussion of MSRP. > > [Juergen] Agree. Would you be ok with adding MSRP in parentheses as > the "accept-types" parameter is MSRP specific? Like > "Thus in the example above, the original attribute line "a=accept- > types:text/plain" is represented by the attribute line "a=dcsa:2 > accept-types:text/plain", which specifies that this instance of the > subprotocol (here MSRP) being transported on the SCTP association > using the data channel with stream id 2 accepts plain text files." > Yes, or like this to avoid the paranthesis: "Thus in the example above from MSRP, the original attribute line "a=accept- types:text/plain" is represented by the attribute line "a=dcsa:2 accept-types:text/plain", which specifies that this instance of the MSRP subprotocol being transported on the SCTP association using the data channel with stream id 2 accepts plain text files." >> >> >> 2. Move the note about MSRP from 5.1.2.1 to the introduction. >> In 5.1.2.1 there is this note: >> ---------------------------------------------------------- >> >> Note: This document does not provide a complete specification of how >> to negotiate the use of a data channel to transport MSRP. Procedures >> specific to each sub-protocol such as MSRP will be documented >> elsewhere. The use of MSRP is only an example of how the generic >> procedures described herein might apply to a specific sub-protocol. >> ------------------------------------------ >> It comes late in the document. I suggest to move it to become a >> paragraph last in the introduction and change it to a regular >> paragraph saying: >> ---------------------------------------------------------------- >> This document makes use of MSRP in many of the examples. It does >> not provide a complete specification of how >> to negotiate the use of a data channel to transport MSRP. Procedures >> specific to each sub-protocol such as MSRP will be documented >> elsewhere. The use of MSRP in some examples is only to show how >> the generic >> procedures described herein might apply to a specific sub-protocol. >> ------------------------------------------------------------------ > > [Juergen] Agree. > >> >> 3. What syntax to use for irrelevant positional parameters in mapped >> RFC 4566 attributes >> We had a discussion about t140-usage-data-channel recently, where the >> mapping of the a=fmtp: of RFC 4103 and RFC 4102 was discussed. >> The attribute was proposed to be coded as an example: >> a=dcsa:1 fmtp:- cps=30 >> >> that is supposed to follow the syntax rule from sdpneg 5.1.2.1: >> dcsa-value = stream-id SP attribute >> attribute = <from-RFC4566> >> >> In sdp, this would be represented by something like >> a=fmtp: 102 104/104/104 cps=30 >> if the payload type 102 represented red payload >> >> it could also be represented by >> a=fmtp: 99 cps=30 >> if the payload type 99 represented t140 payload >> >> Question: >> Is the single "-" sufficient to describe that some parameters are >> ignored? >> >> Proposal: >> Since a=fmtp is a very common RFC 4566 attribute, describe a syntax >> for its use explicitly in sdpneg. > > [Juergen] In the T.140 over data channel case I assume that "-" as the > a=fmtp attribute's "fmt" > value would actually be sufficient. This specific case should probably > be described in draft-schwarz-mmusic-t140-usage-data-channel. > > a=fmtp is indeed a common attribute, which is often used on RTP based > SDP media descriptions. > However, I am not sure how many of such RTP based media formats could > eventually be also transported over a data channel, in addition to T.140. > Would we actually be able to formulate a generic rule covering all > potential dcsa encapsulated fmtp usage cases? > I would assume that such media format specific RTP to data channel > interworking case would be described in dedicated documents, > which then would also describe the media format specific encapsulation > of the fmtp attribute (if this is then still used in case of > data channel transport). > Yes, I reread RFC 4566 and realized that the "-" is a syntactically correct <fmt>. So, I accept that draft-schwarz-mmusic-t140-usage-data-channel should specify the specific mapping cases to RFC 4102 and RFC 4103. > >> >> 4. Many subprotocol-unspecific attributes also fit the pattern in 5.1.2 >> Section 5.1.2 has the name "subprotocol specific attributes". >> There are many general attributes defined in RFC4566 and elsewhere >> that apply to many subprotocols. >> It may be subprotocol specific if they are applicable to each >> subprotocol, but they are not specified in a subprotocol-specific RFC. >> An example is "lang" from RFC 4566 that is right now discussed in the >> slim group ( as well as its proposed addition "humintlang" ). >> >> Can section 5.1.2 be called "Other media level attributes" in order >> to surely include these quite generally applicable attributes. Some >> further adjustments in the text would also be needed. > > [Juergen] Agree. > >> >> Maybe the last words in 5.1.2.1 before the note is intended to say >> this, and could be moved up closer to the beginning of 5.1.2 or >> 5.1.2.1 and adapted to its new place: >> "The same syntax applies to any other SDP attribute required for >> negotiation of this instance of the sub-protocol." > > [Juergen] Yes, agree to moving this sentence up in 5.1.2.1. The first > paragraph of 5.1.2.1 introduces the actual dcsa attribute and outlines > its syntax > (before the syntax is then formally defined after that). Would you be > ok with moving this sentence right after this first paragraph of 5.1.2.1 > (before the formal syntax definition)? > Yes, looks good. Thanks, Gunnar >> >> >> /Gunnar >> >> _______________________________________________ >> mmusic mailing list >> mmusic@ietf.org >> https://www.ietf.org/mailman/listinfo/mmusic > > > > > _______________________________________________ > mmusic mailing list > mmusic@ietf.org > https://www.ietf.org/mailman/listinfo/mmusic
- [MMUSIC] Comments on mmusic-data-channel-sdpneg-05 Gunnar Hellström
- Re: [MMUSIC] Comments on mmusic-data-channel-sdpn… Juergen Stoetzer-Bradler
- Re: [MMUSIC] Comments on mmusic-data-channel-sdpn… Gunnar Hellström